Because the tag method returns an OrderedDict with labels as keys, it will throw a RepeatedLabelError error when multiple areas of an address have the same label, and thus can’t be concatenated. When RepeatedLabelError is raised, it is likely that either (1) the input string is not a valid address, or (2) some tokens were labeled incorrectly.

RepeatedLabelError has the attributes original_string (the input string) and parsed_string (the output of the parse method on the input string). You can use these attributes to write custom exception handling, for example: